Under what condition can a drum trap be used as a fixture trap?

The use of a drum trap as a fixture trap is permissible when it is serving as an interceptor. This means that such a trap can effectively capture and separate unwanted debris or materials from the wastewater before it enters the drainage system, thereby functioning as a preliminary filtration mechanism.

Drum traps are designed to hold a certain volume of water, which helps to create a seal that prevents sewer gases from entering the building while also providing a space for solids and sediments to settle. When they serve as interceptors, they play a critical role in maintaining the efficiency and cleanliness of the plumbing system.

Other options do not meet the necessary conditions for using a drum trap as a fixture trap. If access for servicing is not needed, it would typically be against best practices, as maintenance is essential for proper function. Saying it is the only option available does not justify its use; proper selection of traps should always be based on function and suitability. Lastly, a drum trap must be installed in a vertical position to achieve proper drainage and function, so a horizontal position would not be appropriate for its use as a fixture trap.